1. Field of the Invention
The present invention relates to sweet taste receptor chimeric proteins, chimeric G proteins, and their uses. A cell that expresses a sweet taste receptor protein or G protein is useful to detect a sweet-tasting substance or a sweet taste-regulating substance, and so forth.
2. Brief Description of the Related Art
The T1R family of receptors are known to be involved in taste perception, and have also been identified as seven-transmembrane G protein-coupled receptors (GPCR). It is known that the T1R family includes three kinds of subunits, T1R1, T1R2, and T1R3, and the heterodimer of T1R2 and T1R3 functions as a sweet taste receptor (Nelson, G. et al., Cell, 106:381-390 (2001) for mouse, and WO2002/064631 for human). It is also known that the heterodimer of T1R1 and T1R3 functions as an umami taste receptor (Nelson G. et al., Nature, 416:199-202 (2002) for mouse, and WO2002/064631). Furthermore, a method has been proposed to detect a ligand compound that specifically binds to a sweet taste receptor, such as a sweet-tasting substance or a substance that regulates sweet taste, by using a cell that expresses a sweet taste receptor and the G protein α subunit (Gα) (WO2002/064631).
Furthermore, a chimeric protein of human T1R2 and mouse T1R2 (Ohta, K., et al., Biochem. Biophys. Res. Commun., 406:435-438 (2011)), and a chimeric protein of human T1R3 and mouse T1R3 (ibid. and Jiang and P. et al., J. Biol. Chem., 279(43):45068-45075 (2004)) have been produced, and a cysteine-rich domain (CRD) has been identified as being necessary for perception of sweet taste. However, it is not known whether or not a chimeric T1R2 or chimeric T1R3 having a specific structure is more suitable for detection of a sweet taste receptor-activating substance as compared to naturally occurring T1R2 and T1R3.
As taste-specific G proteins, the Gq family, gustducin, transducin, and so forth, are known, and gustducin and transducin have been reported to have the same function when interacting with a receptor (Hoon, M. A. et al., Biochem. J., 309:629-636 (1995)).
As for Gα, a chimeric protein consisting of a mutant Gαq protein in which the C-terminal part is replaced with 44 amino acid residues of the C-terminus of the mouse transducin α subunit has been reported (WO2002/036622). It is disclosed that this chimeric protein shows increased promiscuity (WO2002/036622). In addition, this reference describes that the amino acid residues of the C-terminus of the transducin α subunit to be used should be 44 residues or less.
Furthermore, a chimeric G protein consisting of the rat Gα15 protein in which the last 44 amino acid residues are replaced with the last 44 amino acid residues of the gustducin α subunit has been reported (WO2004/055048).